Evidence is presented that a substance of pineal origin-different from melatonin-exerts a potent influence in normal reproductive physiology. One site of action of this antigonadotropic substance is at the level of the pituitary gland where it acts as an inhibitor to luteinizing hormone-releasing factor (LRF). The proposed application will determine whether a single pineal cell type or two different cell types are involved in the synthesis of indoleamines (melatonin) and production of an LRF-inhibitory factor (LRF-IF). The relationship of noradrenergic terminals to a specific cell population(s) will be examined. The methods employed include immunocytochemical identification and localization of each tissue antigen (melatonin and LRF-IF) and histofluorescence of catecholamines. The design for this study will examine normal rat pineal glands and glands in vitro. Morphological data will be corroborated with predicted biochemical events in cultured glands.